A. Field of the Invention
This invention relates to novel fiber-forming terpolyamides which are prepared by melt polymerization techniques and have melting points (Tm) below 320.degree. C., glass transition temperatures (Tg) above 115.degree. C. and good thermal stabilities.
B. Description of the Prior Art
Copolymers prepared by the melt polymerization of a mixture (e.g. 60/40) of hexamethylene diammonium terephthalate and hexamethylene diammonium isophthalate (i.e. 6T and 6I salts) and the melt spinning of each 6T/6I copolymers into useful fibers are described in U.S. Pat. Nos. 3,941,744; 4,022,756 and 4,113,708.
Although 100% 6T polymer (i.e. polyhexamethylene terephthalamide) has a high Tg, it also has a Tm too high (above 320.degree. C.) for it to be easily melt processed. While replacing a portion of the terephthalic acid with isophthalic acid lowers the Tm while preserving the high Tg, the resulting 6T/6I copolymer, lacks crystallinity.
Terpolymers produced from 6T salt, 6I salt and hexamethylene diammonium adipate (66 salt) are described in British Pat. No. 1,526,329. Although these terpolymers have lower melting points and are easier to melt process than 6T/6I copolymers at the same 6T concentration, they have reduced thermal stability.
It is an object of the present invention to provide fiber-forming polyamides having high Tg values, melting point values below 320.degree. C., and better thermal stabilities than 6T/6I/66 terpolymers.
It is a further object of the invention to provide fiber-forming polyamides of the foregoing description which can be prepared by melt condensation from aqueous solution of the appropriate salts or monomers.
Other objects and advantages of the invention will become apparent to those skilled in the art from the following description.